Relevant prior art references for providing a full understanding of the use of bio-organic and wastewater sludges as beneficial soil or fertilizers for agricultural lands and processes for the production of treated sludges include U.S. Pat. Nos. 4,781,842; 4,902,431; 5,275,733; 5,417,861; 5,853,450; 5,853,590; 6,248,148 and 6,407,038; and references contained therein.
Of particular mention is U.S. Pat. No. 5,853,590 which describes a method of treating sludge to provide a stable product for use as a beneficial soil or fertilize for agricultural lands, which includes the steps of (a) mixing sludge with at least one alkaline material in an amount sufficient to raise the pH of the mixture to a level of at least 12 and to increase the percent of solids in the mixture to at least 40% by weight, and such that the odorant sludge organics and inorganics are bound to adsorbent particles of the alkaline material, (b) aerating and drying the mixture by agitation and heating to stabilize the mixture and increase the percent solids to at least 50% by weight, and (c) pasteurizing the dried mixture at a temperature at or above 52.degree. C. by application of heat resulting from an exothermic reaction of the alkaline material with water in the sludge, wherein said step (b) is carried out in a mechanical means selected from the group from the group consisting of a drum dryer, a pelletizer, and a fluidized bed apparatus, and wherein the heat applied for drying in said step (b) reduces the amount of additional heat required for pasteurization in said step (c) thereby reducing the amount of alkaline material needed for said exothermic reaction.
Wastewater sludge is a sludge comprised of the solids portion of the inflow of a wastewater treatment plant that normally is comprised of microorganisms, organics and inorganic precipitates that are separated from the water effluent discharge from the plant. This sludge is often unprocessed beyond a concentration process and is termed a raw sludge. Other sludges from a wastewater plant have been processed and are considered digested sludges or secondary or waste-activated sludges or combined sludges.
Bioorganic sludge is an organic sludge comprised of a material or materials selected from the group: sludges resulting from production of antimicrobials and other pharmaceutical products, bacterial fermentation sludges, sludges resulting from production of beer and wine, mushroom compost waste, paper mill sludges, sludges that contain microorganisms that have resulted from recycled organic products such as paper products, sludges resulting from the growth of microorganisms for the production of chemicals and organics, industrial sludges and byproducts resulting from the production of microbial products and foodstuffs, sludges resulting from the animal slaughter industry—particularly if these are digested or otherwise broken down by microorganisms.
Organic sludge is a sludge derived from industrial products and byproducts that are comprised in the majority microbially degradable organic materials not of biological or microbiological origin. This definition would include sludges comprised of recycled organic products such as recycled paper and paper products.
Preliminary or pretreatment is the very first stage of sludge treatment, involving, the removal of larger materials and grit that if not removed could hinder subsequent treatment processes. It is accomplished through the use of equipment such as bar screens, macerators, comminutors, racks and grit removal systems.
Primary treatment is usually comprised of preliminary treatment followed by primary clarifiers which remove approximately 50% suspended solids and 35-40% B.O.D.5. This is accomplished by channeling flows through large tanks with residence times of 2-4 hours, thus allowing suspended solids to settle. Post disinfection and a biosolids treatment process are normally included. Enhanced Primary Treatment can be performed by the addition of a coagulant such as ferric chloride along with a polymer, improving the degree of S.S. and B.O.D. removal to 80% and 60% respectively.
Secondary treatment involves a primary process and a biological treatment stage. There are many biological processes in the treatment operation with the majority being variations of fixed film and mixed culture applications. The activated sludge process (mixed) is achieved by establishing large diversified cultures of bacteria. The bacteria metabolizes and provides the enzymatic breakdown of organic components, i.e., liquids, carbohydrates, proteins and cellulose, in the wastewater. 90% removal rates of B.O.D. and suspended solids are typical of secondary treatment.
However, although the manufacturing process described in aforesaid U.S. Pat. No. 5,853,590 provides an improvement in the art, it suffers from a drawback of allowing dust particles of the alkaline treated sludge to be carried off during the air-drying step of the process and create an unsafe environment.
Surprisingly, we have discovered that the aforesaid drawback can be overcome by a modification that provides for the prevention of such dust formation.